Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753280AbbLCT0X (ORCPT ); Thu, 3 Dec 2015 14:26:23 -0500 Received: from mail-yk0-f179.google.com ([209.85.160.179]:36274 "EHLO mail-yk0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752895AbbLCT0U (ORCPT ); Thu, 3 Dec 2015 14:26:20 -0500 Date: Thu, 3 Dec 2015 14:26:16 -0500 From: Tejun Heo To: Peter Zijlstra Cc: Ulrich Obergfell , Ingo Molnar , Andrew Morton , linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue Message-ID: <20151203192616.GJ27463@mtj.duckdns.org> References: <20151203002810.GJ19878@mtj.duckdns.org> <20151203093350.GP17308@twins.programming.kicks-ass.net> <20151203100018.GO11639@twins.programming.kicks-ass.net> <20151203144811.GA27463@mtj.duckdns.org> <20151203150442.GR17308@twins.programming.kicks-ass.net> <20151203150604.GC27463@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151203150604.GC27463@mtj.duckdns.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2626 Lines: 80 Task or work item involved in memory reclaim trying to flush a non-WQ_MEM_RECLAIM workqueue or one of its work items can lead to deadlock. Trigger WARN_ONCE() if such conditions are detected. Signed-off-by: Tejun Heo Cc: Peter Zijlstra --- Hello, So, something like this. Seems to work fine here. If there's no objection, I'm gonna push it through wq/for-4.5. Thanks. kernel/workqueue.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2330,6 +2330,37 @@ repeat: goto repeat; } +/** + * check_flush_dependency - check for flush dependency sanity + * @target_wq: workqueue being flushed + * @target_work: work item being flushed (NULL for workqueue flushes) + * + * %current is trying to flush the whole @target_wq or @target_work on it. + * If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not + * reclaiming memory or running on a workqueue which doesn't have + * %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to + * a deadlock. + */ +static void check_flush_dependency(struct workqueue_struct *target_wq, + struct work_struct *target_work) +{ + work_func_t target_func = target_work ? target_work->func : NULL; + struct worker *worker; + + if (target_wq->flags & WQ_MEM_RECLAIM) + return; + + worker = current_wq_worker(); + + WARN_ONCE(current->flags & PF_MEMALLOC, + "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%pf", + current->pid, current->comm, target_wq->name, target_func); + WARN_ONCE(worker && (worker->current_pwq->wq->flags & WQ_MEM_RECLAIM), + "workqueue: WQ_MEM_RECLAIM %s:%pf is flushing !WQ_MEM_RECLAIM %s:%pf", + worker->current_pwq->wq->name, worker->current_func, + target_wq->name, target_func); +} + struct wq_barrier { struct work_struct work; struct completion done; @@ -2539,6 +2570,8 @@ void flush_workqueue(struct workqueue_st list_add_tail(&this_flusher.list, &wq->flusher_overflow); } + check_flush_dependency(wq, NULL); + mutex_unlock(&wq->mutex); wait_for_completion(&this_flusher.done); @@ -2711,6 +2744,8 @@ static bool start_flush_work(struct work pwq = worker->current_pwq; } + check_flush_dependency(pwq->wq, work); + insert_wq_barrier(pwq, barr, work, worker); spin_unlock_irq(&pool->lock); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/